Peter Bielenberg, who has died aged 89, was a member of the internal German resistance to Nazism and was sent to a forced-labour camp after the abortive July 1944 coup against Hitler. This story provided the climax of The Past Is Myself (1968), the bestselling autobiography of his British wife Christabel, who lived through the war in Germany.

Bielenberg was active in the Kreisau circle, which became the focus of German upper-class and intellectual opposition to the Nazi movement. It was his close association with Adam von Trott zu Solz, one of its heroes, that led to Bielenberg's arrest and imprisonment without trial. Despite the moral and physical courage of such individuals, the opposition to Hitler - once the left had been suppressed and the Wehrmacht seduced with prospects of expansion and conquest - was not only modest but had much to be modest about.

The objections of the upper-class opposition to Hitler were initially more moral and aesthetic than practical, though they were seen as no less dangerous. The dissidents despised the petty-bourgeois respectability in which the Nazis clothed their excesses. Initially, the Kreisau circle's principal aim, fatuous in retrospect, was to persuade likeminded Wehrmacht officers and influential foreign, especially British, sympathisers to warn Hitler off.

Only in 1943, when it became obvious that Germany could not win the second world war, did the resisters accept that they might as well be hanged for a sheep as for a lamb, and turned their minds to armed revolt. But, in July 1944, Claus von Stauffenberg's bomb failed to kill Hitler.

Bielenberg was born in Hamburg, the son of the head of a prosperous law firm, in whose footsteps he was meant to follow. He was only 20 when he met the well-connected, Anglo-Irish Christabel Burton, nearly three years his senior, who had given up an Oxford scholarship to study singing in Hamburg. Ironically, Bielenberg, who had been awarded a scholarship to the United States, lost it in 1933, when the Americans expressed a preference for a representative of the "new Germany" - a Nazi.

Both tall and elegant, Bielenberg and Christabel danced exceptionally well together, and married in September 1934, despite misgivings in both their families. The new Frau Bielenberg thereupon chose to become a German citizen by naturalisation.

In an early example of their blithe, upper-class assumption that it was not what you knew but who you knew that mattered - an instinct often proved right, even under Nazism - Bielenberg wangled an attachment to the German embassy in London as part of his work experience as a trainee lawyer. He and his wife then moved to Hamburg, until he got his law doctorate in 1937 and joined the family firm.

The following year, he secured the acquittal of a socialist on a charge of distributing illegal pamphlets - but was shocked when his client was arrested and taken away immediately afterwards. At that point, the couple wanted to emigrate to neutral Eire, but Trott dissuaded them.

Instead, early in 1939, they moved to Berlin, where Bielenberg, with extreme distaste, joined the Nazi party in order to take up a civil-service post. During a holiday in England that August, he visited his wife's highly-placed contacts - she was related to the Harmsworths, making her a niece of the press Lords Northcliffe and Rothermere. Like Trott, who undertook similar missions, Bielenberg looked, in vain, for prominent, non-political Britons to warn Hitler against invading Poland. They got back to Germany just in time for the outbreak of war in September.

The dissidents, organised into a communist-style cell system, continued to meet in the Bielenbergs' huge apartment, where there were no neighbours to overhear their agonising about how to stop Hitler. They still placed their hope in German generals and foreign - particularly American - intervention in the war, rather than in the possibility of direct action of their own.

Through contacts, Bielenberg wangled his way out of his ministry - and military - service into war-work in industry. When he was posted to eastern Germany, Christabel took their children to the Black Forest, and the couple saw little of each other until the last days of the war.

The Gestapo closed in on the dissidents even before July 1944; afterwards, hundreds were arrested, and the ringleaders hanged by piano-wire after macabre show trials. Bielenberg, whom Trott had tried hard to reach just before the bomb plot, was held on suspicion of treason, just as he was preparing to raid the armoury at his Prussian factory for weapons with which to snatch his friend from prison.

Christabel, accustomed to pulling strings and getting her own way, used her contacts to get Peter transferred from the east to Berlin. But after six weeks he was sent to Ravensbruck, a forced-labour camp for women, 50 miles north of Berlin, and was confined in the SS punishment block.

A furious Christabel now decided to tackle the Gestapo officer responsible for Peter's interrogation, giving him such a dressing-down that he promised to get her husband out of the camp before he left for the eastern front. Bielenberg was released to a punishment company, but escaped to join his family in the Black Forest, where he hid until the fighting ended in May 1945.

After the war, Christabel's indefatigable string-pulling ensured that her husband was the first German civilian to get a permit to go to Britain. Once he had recovered from a serious motor- cycle accident, they and their three sons emigrated to Ireland in 1948 and took up farming in County Carlow.

Bielenberg approached this new challenge with a thoroughness worthy of the Prussian general staff, reading up on agriculture and finance while commissioning locally unheard-of soil tests. The resulting well-chosen fertilisers transformed a dilapidated and exhausted farm into a commercial success.

As they settled amid Christabel's vast extended family, to which their own children and grandchildren added in due course, Peter seemed content to fade into the background, even when his wife's wartime memoir became a runaway bestseller. She survives him, as do their children.

 Peter Bielenberg, lawyer, farmer and wartime dissident, born December 13 1911; died March 13 2001